Morris Minor Owners Club

I think it also depends on the make of pump.

There are repro pumps on the market for various cars and they come from India. We had a similar issue here recently with an MG pump which didn't fit directly.
Regards
Declan

On the question of fuel level in the float chamber: I've adjusted several carbs where the fuel level was, in practice, too high. Bear in mind that the "drill bit" method only sets the position of the top of the float, and you're not actually checking the petrol level. So if, for instance, petrol is less dense than it used to be, it will need to come further up the float than it used to. If the petrol level is too high, it's more likely to splash around and show round the edge of the lid, and, more importanly, to dribble from the mouth of the jet when the engine is stationary.

But won't it do awful things to the mixture if the fuel level is too low? Within reason, no. There's a mighty suck under the carburettor piston when the engine is running, so having to lift the petrol a fraction of an inch more isn't going to make any difference. Do the maths for the suck needed to lift that weight of carburettor piston and you'll see.

So bend that float chamber lid forked thing a bit more - use a bigger gauging rod than the book says.

Kevin

Cheers Kevin

It's definately a fine balance thing. I've tried the float arm from my old H1 carb - 7/16" gap as opposed to 5/16"and it ran dry almost straight away. I've ordered a new float needle and seat today, even though the one I've been trying is just a year old. That, plus some fractional fiddling of the float arm should hopefully solve the problem.

On the plus side the new water pump is now installed and leak free.

Regards, Paul

If the forked arm of the float chamber is bent in the wrong place, it doesn't push vertically on the valve. This can make it jam in either open or closed positions. Another reason for the valve sticking is if it's been installed with the wrong tools. I believe SU (Burlen) sell a box spanner, or you can use a close-fitting deep socket. but an open-ender, pliers, stillsons, or a mole wrench can distort the valve body.

Kevin

Stillsons !! Hahahahahahaha - would need to be the tiniest set in the world!

Should have made it clearer: mole wrench on the valve body, stillsons to turn the lid.

And I should have added "cold chisel" to remind us of steering wheel nuts....

Kevin

"Screwdrivers are for taking them out"

If you listened closely this morning you'd have heard an infuriated Gaaaah! Coming from Suffolk. New float needle and seat inserted. Same weep coming from chamber gasket. Adjusted float arm to various configurations, no difference; oddly even if set to run dry the same weep develops before the engine dies (I say weep, its almost like vapour that squeezes out from the rim and then sits on the chamber lid, gradually seeping down the chamber body at idle). I've cleaned up both the lid and the chamber rims and the float seems okay. I've examined it to see if the needle is not fouling and it seems okay too. When I blow through the pipe into the needle seat with the lid upside down the needle still seals. Is it possible that the lid is slightly distorted or worn somewhere or am I being overly paranoid about this and should just live with it?

Paul

It should be bone dry. What pump do you have ?

Electronic 'black box' type - fitted to the car when I got it. It seems to work fine and doesn't seem to be overloading the chamber: When I remove the lid the chamber is by no means full - certainly not to the level of the brim. Top of the float is probably about 1/2" down from it, petrol level a fraction lower, and the needle seems to have plugged the inlet as there is still fuel in the inlet tube after I remove the fuel line. There's no evidence that petrol is running down the outside of the seat and along the bottom of the lid, it's very secure and tightly fitted and around the bleed hole is dry.

No idea what a 'black box' pump is - but probably it's pumping at too high a pressure and the fuel is splashing out into the float chamber. Good old SU points pump is what you should have.

Black box is a term used by philosophers of science to describe an event that is too complicated to explain quickly or if they dont know what happens to change something. I used it because I have no idea what happens inside the sealed electronic cylinder to suck in and pump out the fuel - it just does! There was no sign of any leakage from the previous H1 carb chamber for the 803 engine which worked well, so I'm not convinced it is the pump, though cant rule it out I suppose. Back to it again today...

Black box is a term used by engineers to describe boxes of a very dark hue

My engineer dad used to refer to tools by colour and description: 'Pass me the blue wotsit (wrench)' and 'that windey thing with the little black knob' (ratchet). Worryingly he was building Rolls Royce jet engines...

I agree with Roy on this one: an SU low pressure pump uses a very light return spring, as the petrol will virtually syphon out of the pump on the delivery stroke. Most alternative pumps seem to have much higher delivery pressure unless you add yet another thing to go wrong or leak - a pressure regulator. Even if you mount the new pump by the tank, the extra couple of feet of delivery height is only equivalent to less than one psi or so.

Clearly it's not completely overcoming the float chamber valve, or the stuff would be peeing everywhere, but it may be enough to let a few drops extra past. It's extremely difficult to measure the fuel level directly with any accuracy - how much do you press on the float to simulate the load the valve and weight of the fork impose on it? A better check might be to remove the suction chamber, pisto, and needle so that you can see the top of the jet tube. Turn the ignition on and watch for any fuel appearing at the top of the jet - but it's difficult to see, and a bit of tissue may be the only way to detect it.

Kevin

Hello Marky,

"Black box is a term used by engineers to describe boxes of a very dark hue"

Not always, aviation black boxes are orange. I was told that they (Flight data recorders) were thought of by a Dr. Edwin Black, but I don't know if that's true or not?

Alec

Hi,
I believe David Warren invented the so called black box.

Roy.

I wasn't thinking that the mystery pump could overcome the float valve - just that if the pressure is high - when the valve opens, the petrol could be spraying in and thus splashing up and showing as a witness mark on the float bowl.

Well, following on from all the interesting technical stuff I did something non-technical in a moment of trial and error. I took the brass float out and turned it the other way up, the more rounded side facing upwards. Unbelievably there is no longer a weep and the gasket is dry, with ample fuel reaching the engine. If there is an algorithm for cups of tea drunk/hours spent fiddling to solving of problem I think I'm off the scale on this one.

Thanks all for the advice; lots learnt along the way.

Paul